**phase** returns the phase of //number// (the angle part of its polar representation) in radians, in the range ''​-π''​ (exclusive) if minus zero is not supported, or ''​-π''​ (inclusive) if minus zero is supported, to ''​π''​ (inclusive). The phase of a positive //​[[CL:​Glossary:​real]]//​ number is zero; that of a negative //​[[CL:​Glossary:​real]]//​ number is ''​π''​. The phase of zero is defined to be zero.

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If //number// is a //​[[CL:​Glossary:​complex float]]//, the result is a //​[[CL:​Glossary:​float]]//​ of the same //​[[CL:​Glossary:​type]]//​ as the components of //number//. If //number// is a //​[[CL:​Glossary:​float]]//,​ the result is a //​[[CL:​Glossary:​float]]//​ of the same //​[[CL:​Glossary:​type]]//​. If //number// is a //​[[CL:​Glossary:​rational]]//​ or a //​[[CL:​Glossary:​complex rational]]//,​ the result is a //​[[CL:​Glossary:​single float]]//.

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The branch cut for **phase** lies along the negative real axis, continuous with quadrant II. The range consists of that portion of the real axis between ''​-π''​ (exclusive) and~''​π''​ (inclusive).